1. Field of the Invention
The present invention relates to a phosphor which is excited by light with a wavelength of 254 nm, for example, in a mercury discharge tube, to emit near infrared rays having maximum intensity at about 750 nm.
2. Description of the Prior Art
Many different office machines have been developed and utilized in various fields as a result of the remarkable recent developments in electronic technology. One such office machine is an optical code reader (referred to as OCR). In some previously used OCRs an incandescent lamp or a halogen lamp has been used as the light source for reading the code. However, the efficiency of such light sources is low, whereby power consumption has been disadvantageously large and heat output disadvantageously high. Therefore, fluorescent lamps which emit dark red light have come into use.
The phosphors currently used for such fluorescent lamps have several disadvantages in view of the efficiency and emission output maintenance factor of the lamp. When a sheet having many printed colors is read out by an OCR having a fluorescent lamp in which a previously disclosed phosphor is used, the OCR reads out not only written codes, but also the printed frame and symbols. Accordingly, only sheets having limited color could be used.